1. Technical Field
The present invention relates to an inertial sensor.
2. Description of the Related Art
Recently, an inertial sensor has been used as various applications, for example, military such as an artificial satellite, a missile, an unmanned aircraft, or the like, vehicles such as an air bag, electronic stability control (ESC), a black box for a vehicle, or the like, hand shaking prevention of a camcorder, motion sensing of a mobile phone or a game machine, navigation, or the like.
The inertial sensor generally adopts a configuration in which a mass body is adhered to an elastic substrate such as a membrane, or the like, in order to measure acceleration and angular velocity. Through the configuration, the inertial sensor may calculate the acceleration by measuring inertial force applied to the mass body and may calculate the angular velocity by measuring Coriolis force applied to the mass body.
In detail, a scheme of measuring the acceleration and the angular velocity using the inertial sensor is as follows. First, the acceleration may be calculated by Newton's law of motion “F=ma”, where “F” represents inertial force applied to the mass body, “m” represents a mass of the mass body, and “a” is acceleration to be measured. Among others, the acceleration a may be obtained by sensing the inertial force F applied to the mass body and dividing the sensed inertial force F by the mass m of the mass body that is a predetermined value. Further, the angular velocity may be calculated by Coriolis force “F=2 mΩ×v”, where “F” represents the Coriolis force applied to the mass body, “m” represents the mass of the mass body, “Ω” represents the angular velocity to be measured, and “v” represents the motion velocity of the mass body. Among others, since the motion velocity V of the mass body and the mass m of the mass body are values known in advance, the angular velocity Ω may be calculated by detecting the Coriolis force (F) applied to the mass body.
Meanwhile, as described in Korean Laid-Open Patent Publication No. 10-2011-0072229, the inertial sensor according to the related art includes a member bonding a mass body to a flexible membrane such as a diaphragm, or the like, and piezoelectric elements and upper/lower electrodes above the membrane so as to drive the mass body or sense a displacement of the mass body. However, in the inertial sensor according to a prior art, the upper electrode formed on the piezoelectric element is patterned and thus, the piezoelectric element is not encapsulated. Therefore, water or humidity may be permeated into the piezoelectric element. As a result, if water or humidity is permeated into the piezoelectric element, physical properties may be changed or the piezoelectric element may be delaminated. Further, the non-encapsulated piezoelectric element may be damaged during a wet process or a dicing process in the manufacturing process of the inertial sensor.